ELEMENTARY 
LATHE PRACTICE 



Elementary Lathe Practice 



AS ADAPTED TO THE TEACHING OF 

MACHINE SHOP PRACTICE 
IN TECHNICAL SCHOOLS. 






BY T. J. PALMATEER 
INSTRUCTOR IN MACHINE WORK 

Leland Stanford Junior University 



Copyright 1917, by T, J. Palmateer 



FIRST EDITION 

1917 

Press of Nolts Bros.o^^^^San Jose, California 







j^'j 



CI.A455285 



JAN 25 1917 



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A 



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PREFACE 

The object of this instruction book is to help beginners to 
acquire some familiarity with the more common lathe operations 
in the shortest practicable period of time. For this purpose three 
exercises have been designed with the view of giving the student 
the maximum amount of information in the small amount of time 
usually allowed for this purpose. The repetition of operations 
has therefore been avoided wherever it was considered advisable 
and the time lost in simply cutting off meta] has been reduced as 
much as possible. 

It is assumed that beginners will receive oral instruction on 
the manipulation of the lathe, as in shifting the belt, the feed con- 
trol, etc. It will also be necessary for the instructor to give a 
practical demonstration of most of the operations. 

The lathe speeds for the different operations as indicated in 
this book are only approximately correct since the actual cutting 
speed of the tool in feet per minute varies with the size and kind 
of lathe used. The instructor is expected to designate the proper 
speeds although the belt connections given herein will generally 
be close enough for beginners. 

In case it is considered advisable to devote to the elementary 
lathe operations less time than would be necessary to complete the 
three exercises presented herein, very good results can be ob- 
tained if the student will read all of the instructions carefully and 
then do only Exercise No. 1 and piece B of Exercise No. 3. 

The instructions here given are not intended as fixed rules for 
it is recognized that some of the operations may be done by other 
methods with equally good results. 



T. J. PKLMATEER. 



Stanford University, Cal. 
January 1917. 



ELEMENTARY LATHE PRACTICE. 



EXERCISE No. 1 
FIT SHAFT TO COLLAR— RUNNING FIT 

Machine Steel 




Cut off with a power hack-saw a piece of steel 6 1/16 inches 
long from a bar 1 inch in diameter. This will allow 1/16 of an 
inch for finishing the ends and 3/16 of an inch for turning the 
diameter. 

An experienced lathe operator would use a piece of steel 7/8 
of an inch in diameter, but for beginners it is better to use larger 
stock to allow for practice turning. 

CENTERING 



Center both ends in the centering machine. The size of the 
center in this shaft should be from 3/16 to 1/4 of an inch in 
diameter. Larger work should have deeper centers. 




F=\ 



,'Driil and Countersink 



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Fig. 1 



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(^:ffl 




Steady Rest M- 

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ff 



Fig. 2 



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a: 



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ELEMENTARY LATHE PRACTICE. 



If a centering machine is not available, the work may be cen- 
tered by first locating the center with a pair of dividers and cen- 
ter punch and then using a combination drill and countersink in 
the lathe as shown in Fig. 1. In this case the work is held by 
hand to prevent it from turning. As this work is to be turned, it 
is necessary to center it only approximately true. 

Accurate Centering. — When the work is to be centered accur- 
ately, it may be done by putting one end in the lathe chuck and 
the other in a steady rest. A pointed tool is then used in the tool 
post as shown in Fig. 2. The point of this tool has an angle of 60 
degrees, the same as the lathe centers, and is ground like a flat 
drill so that it cuts on both sides. 

After the shaft is centered with this tool, a center hole about 
1/8 of an inch in diameter should be drilled. This is done by 
holding the drill in the tail-stock of tne lathe with a drill-chuck, 
as shown in Fig. 3. The object of this center hole is to give the 
center of the shaft a bearing on the lathe center a short distance 
back from the point, as at A in Fig. 4. 

PLACING WORK IN LATHE 

The work is made to rotate on the lathe centers by fastening 
a lathe dog to the shaft at the head-stock end, as shown at A in 



Head Stock 




Tail Srock 



Fig. 5 




Fig. 5. 

The tail-stock center is adjusted so that the shaft will rotate 
freely, yet be tight enough to allow no slack, or lost motion. Since 
the shaft rotates on this center, it should be kept well lubricated 
by using machine oil, or a mixture of graphite and oil. 

To get the best results in turning this sort of work, it is neces- 
sary to face both ends before turning and to rough turn the whole 
piece to within about 0.03, or 0.04 of an inch of the finished size 
before any part of it is finished. However, it is not always neces- 
sary to do this. The object of first rough turning the shaft all 
over is to remove the internal strains of the steel and to wear the 
centers down to a good bearing before any flushing cuts are 



ELEMENTARY LATHE PRACTICE. 



taken. The purpose of facing the ends is to get them square, or 
true, and smooth. 

FINISHING END OP SHAFT 

To face the ends, use a regular turning tool starting to cut 
from the outside and feeding by hand towards the center with the 
cross feed. Such a tool will leave a ridge near the center, as 
shown in Fig. 6. This ridge is cut off with a sharp pointed, side 
cutting tool, as shov^^n in Fig. 7, which is also used for taking the 





finishing cut across the whole end of the bar. When taking this 
finishing cut, lard oil, or some other lubricant, should be used. 

After the finishing cut has been taken, any small ridge, or fin 
that remains at the edge of the center is removed by slightly 
changing the angle of the tool in the tool post and allowing about 
1/64 of an inch play between the centers. Having the work loose 
like this when the lathe is running, allows the extreme point of 
the side tool to extend beyond the edge of the center and cut a 
smooth end. 

The lathe should run slow for the finishing cut and fast when 
the regular turning tool is used. 

TURNING THE SHAFT 

The first, or roughing cut, is taken with a high speed steel 
tool, or bit, fastened in a tool holder. The tool holder is clamped 
in the tool post of the lathe so that the point of the tool is at, or 
a little above, the center, or axis, of the lathe, as in Fig. 8. 

If the point of the bit is too high, it is easy to see that, as the 
shaft rotates, the tool will not cut at all. Fig. 9. In case the tool 
is set below the center, the cutting action is very poor so that 
turning tools are never set as in Fig. 10. 



8 



ELEMENTARY LATHE PRACTICE. 





Fig. 6 



Tig. 9 



Fig 10 




ri9 If 

Turning Toof 




Speed of the Lathe. — In taking the heavy roughing cuts, the 
belt may be placed on the second largest step of the cone, while 
for the finishing cuts the lathe should run a little faster, say with 
the belt in the next smaller step. 

Grinding Turning Tool. — The front, or point, and the sides of 
the tool are ground at an angle, which is called the clearance. If 
the tool has too little clearance, it will not cut freely, while if it 
has too much clearance, the point will be so thin that it will break 
off or become dull quickly. 

The top of the tool is also ground at an angle. This is called 
the rake. If the tool has too little rake, it will not cut freely and 
if it has too much, the edge will soon break down. 

It requires some practice for a beginner to learn the proper 
rake and clearance that should be given to a tool. Fig. 11 shows 
a tool ground with clearance and rake that will give very good 
results. 

Direction Tool Should Travel.— The depth of the first cut 
should be about 1/16 of an inch and the travel of the tool should 
always be from the tail-stock end towards the head-stock. If the 
travel is in the opposite direction, the pressure on the tail-stock 
center is increased, causing it to heat quickly. 

The length of the cut should be as great as possible without 
the lathe dog striking the tool, or cross-rest. 

Adjusting the Lathe to Turn Straight.— After the first cut, 
the work should be calipered and if it is not the same diameter 



ELEMENTARY LATHE PRACTICE. 



at both ends the tail-stock should be adjusted so that the lathe 
will turn straight. 

The tail-stock adjustment is made by loosening the main 
clamping nut B and one of the screws C and then tightening the 
other screw C on the opposite side of the tail-stock, Fig. 5. 

If the shaft is larger at the tail-stock end, the tail-stock should 
be moved towards the front of the lathe one half the difference 
between the diameters of the shaft at the two ends. 

In doing close work, the tail-stock should be adjusted as 
closely as possible, but in this case if it is off center only a little, 
say 0.002 or 0.003 of an inch, it will be close enough providing it 
is set so that the shaft will be turned larger at the head-stock end. 
If the tail-stock is set so that the shaft is turned larger at the tail- 
stock end, the shaft will be too small at the other end after the 
finishing cut is taken. 

Fitting Shaft to the Collar. — After the roughing cut is taken 
and the lathe has been adjusted so that it turns approximately 
stra ght, the end of the shaft is turned for about Vi of an inch so 
that it w 11 just fit the hole in the collar, shown in the drawing 
of Exercise 1. To measure this : first set the inside calipers to the 
dameter of the hole in the collar, then set ^he outside calipers to 
the inside calipers and caliper the shaft as accurately as possible. 
For a final test of this diameter, remove the work from the lathe 
and try it with the collar itself. 

The advantage of turning but i/4 of an inch at the end of the 
shaft is this ; if the finishing cut were set too deep, only 1/4 of an 
inch of the shaft would be too small, while if this cut were taken 
the whole length, the entire shaft would be too small. 

After the shaft has been turned at the end so that it fits the 
collar, the rest of the shaft should be turned a little larger, say 
0.002 or 0.003 of an inch, in diameter. This will leave enough to 
finish with a file. 

Filing. — The object of filing is to take out the tool marks, but 
it is also found to be much easier to make a close fit by filing off 
the last 0.002 or 0.003 of an inch than to take so small a cut with 
a tool. The amount of allowance for filing depends upon the 
character of the finishing cut. Since the less filing required the 
better, the finishing cut should be made as smooth as possible. 

The tool used for the roughing cut may also be used for fin- 
ishing, but it is usually necessary to re-sharpen it. After it is re- 
set in the tool post, the point should be flattened a little wider 



10 



ELEMENTARY LATHE PRACTICE. 



than the pitch of the feed, say about 1/32 of an inch, and parallel 
with the work. This is done with an oilstone. 

For filing work on a lathe, a single cut file is used. This is 
called a lathe, or mill file. 

The stroke of the file should be slow, steady, and straight 
across the shaft. The lathe should run a little faster for filing 
than for turning, the object being to have the work make several 
revolutions for a single stroke of the file. If the lathe runs too 
slow and the stroke of the file is too fast, the shaft, instead of 
be-Ug filed round, will have a series of flat places on the surface. 

After the work is finished as close to the dog as possible, re- 
verse it in the lathe and finish that part where the dog was fast- 
ened. 



EXEECISE No. 2, 




llThrda perl" R.M. 



13Thrds per 1"RH 



The finished shaft in Exercise No. 1 may be used for Exercise 
No. 2. 

Place the shaft in the bench vise and with a rule and scriber 
lay off the dimensions: 1% in., 3 in., and 1% in. Then center 
punch the lines just deep enough so that they can be easily seen 
when the work is in the lathe. 

Turn the large end first. 

When it is necessary to turn a fixed distance, or to a line as 
in this case, it is well to disconnect the feed when the tool is with- 
in about 1/8 of an inch from the end of the cut and to feed the 
tool the rest of the distance by hand. If this is not done, the tool 
may travel farther than it is intended to. 

It is better to turn the portions to be threaded a little under 
rather than over size. For if they are over size, the threads will 
not fit the standard size nut, but if under size the threads do not 
need to be cut so deep in order to fit the nut. 

For measuring the diameters of this piece set the calipers, as 



ELEMENTARY LATHE PRACTICE. 



11 



accurately as possible by measuring from the end of the rule, as 
shown in Fig. 12. 





ng.l3 



Cutting Recess. — The surface at the end as well as the recesses 
between the threads and the taper are cut with a square-nose, or 
cutting-off tool. Fig. 13. 

This tool shoull have a sharp smooth edge, the point being set 
level with the center of the lathe. 

To produce a smooth finished surface lard oil should be used 
with a slow feed and lathe speed. 

After the end is turned to size, reverse the work in the lathe 
and turn the other end and the taper before cutting the threads. 

Turning Taper. — The drawing calls for a taper of 1 inch per 
foot. This is cut by using a taper attachment, or by setting the 
tail stock off center. As most lathes are not provided with a 
taper attachment, the latter method will be used. 

If the work was 12 inches long, the tail stock would be moved 
off center i/^ inch to turn a taper of 1 inch per foot. It being 
only 6 inches long, the tail stock is set off center but half that 
amount, or 14 inch. 

Before taking the finishing cut, caliper both ends to prove 
that the lathe is cutting the correct taper. 

THREAD CUTTING 

The threads are cut to fit 1/2 inch and 5/8 inch nuts having 
United States Standard threads. These threads are flattened at 
the top and bottom to the amount of 1/8 of the pitch instead of 
being sharp pointed as in the case of Standard V-threads. 

Pitch. — The pitch of the thread is the distance from the center 
of one thread to the center of the one adjoining. On the end of 
the exercise having 13 threads per inch the pitch is 1/13 of an 
inch so that the width of the flat at the top and bottom of this 



12 



ELEMENTARY LATHE PRACTICE. 



thread should be 1/8 of 1/13 of an inch, or about .009 of an inch. 

Lead. — The lead of the thread is the distance a nut on the 
screw will travel in making one complete turn. For single threads 
the pitch and lead are the same, but for double threads the lead 
is twice the pitch. 

Grinding Tool.— The sides of U. S. S. threads form an angle of 
60 degrees. To cut this thread in a lathe, a tool the same shape as 
the threads is used. A gauge for grinding this tool accurately is 
shown in Fig. 14. 




If a U. S. S. thread gauge is not available, the tool can be 
ground with the aid of a regular thread and center gauge, shown 
in Fig. 15. With such a gauge the angle can be ground accurate- 
ly, but it will be necessary to measure the flat point with a rule. 

The top of the tool should be ground so that it will be approx- 
imately in a horizontal plane when set in the lathe. 

Where the thread to be cut is as fine as 13 per inch the flat 
surface at the point of the tool is so small that the extreme point 
can be oil-stoned off instead of being taken off with the grinding 
wheel. The flat point should never be wider than the standard 
size, but if it is a little too narrow it will make very little differ- 
ence in ordinary lathe work. 

Setting Tool. — To set the tool so that both sides of the thread 
will have the same angle, the thread gauge is used as shown in 
Fig. 16. The tool should be set on a level with the center of the 
lathe. 

How Lathe is Geared. — To cut 13 threads per inch the work 
must make 13 revolutions while the carriage, which carries the 
tool, travels one inch. For this purpose the lathe spindle is con- 



ELEMENTARY LATHE PRACTICE. 



13 



nected to the lead screw with the proper size gears and the lead 
screw to the carriage by a split nut. This split nut is back of the 
carriage apron and is opened and closed by the lever E, Fig. 17. 



o w 




If the lead screw of the lathe has 6 threads per inch, the gear- 
ing to cut 13 threads per inch must have the same ratio as 6 is to 
13 To cut 16 threads the ratio would be 6 to 16. 

It is not necessary to figure the size of gears for the different 



14 ELEMENTARY LATHE PRACTICE. 



threads as all lathes are provided with an index plate that desig- 
nates the proper size gears to be placed on the stud B and screw 
C, Fig. 17, for the desired thread. 

To Set Change Gear. — To change these gears, first loosen the 
nuts holding the stud and screw gears B and C. Next loosen thfe 
nut G. ThiS will allow the intermediate gear to drop away from 
the stud gear B. Then loosen the nut H so that the intermediate 
gear can be drawn back away from the gear on the lead screw C. 

When the gears are put together, they should be set so that 
there will be a little slack, or lost motion, between the different 
gears. If they are set too close together, they will make a great 
deal of noise when running and there is also danger of breaking 
the teeth. 

While all lathes are not designed alike the method of changing 
the gears is very much the same on all machines except those hav- 
ing the quick change-gear device. With a lathe having such a de- 
vice, instead of changing the gears on the stud and screw the same 
result is obtained by shifting a combination of levers. 

Why Feed Should Be Disconnected. — The mechanism that 
controls the feed, or travel, of the tool when cutting threads is 
independent of that used for the feed when doing plain turning. 
The two feeds usually run at different speeds so that if they are 
both in action at the same time the gears in the carriage will 
break. For this reason all lathes are provided with some means 
of disconnecting the feed used for plain turning when cutting 
threads. 

To disconnect the feed on the lathe shown in Fig. 17, move the 
lever J to the central, or neutral, position. This should always 
be done before starting to cut the threads. 

Speed of Lathe. — The lathe should run slower for cutting 
threads than for plain turning. With most lathes if the belt is 
on the largest step of the cone it will give about the right speed 
for cutting the threads in this exercise. 

The object of running the lathe slow is to give the operator 
time to draw back the tool at the end of the cut and to obtain a 
smoother cut. If the speed of the lathe is too fast, the cutting 
action will be so quick that the tool, instead of cutting clean and 
smooth, will tear out the metal leaving a rough surface. 

The slower the lathe runs the easier it is to cut the threads, 
but it will also take longer to do the job. It therefore requires 



1 



ELEMENTARY LATHE PRACTICE. ^5 



practical experience to determine tiie proper speed to be used for 
cutting the different size threads. 

Chamfering. — After the lathe and tool are properly set, cham- 
fer off the sharp corners where the threads begin and end with 
the side of the thread tool. The depth of this cut should be about 
the same as that of the threads when finished. Tf the corners are 
not chamfered, the threads, when cut, will form a very thin edge, 
or fin, at the ends. 

Use of Adjustable Stop.— To regulate the depth of each cut 
an adjustable stop is used as shown at K. First move the tool so 
that the point just touches the work, then adjust the screw on 
the attachment K so that the cross-rest will not go in any farther. 
Now move the carriage by hand until the point of the tool is a 
little past the tail-stock end of the work ; close the split nut on 
the lead screw with the lever E ; and turn the screw on the at- 
tachment K so that the tool can be moved in just enough to take 
a very light cut. 

Start the lathe and when the tool has reached the end of the 
cut back it out and reverse the lathe. By reversing the lathe the 
tool is returned to the starting po-nt without disconnecting any 
of the gearing. The object of drawing the tool back is to prevent 
it from dragging on the work during its return. 

The tool will never travel over the same path on the reverse 
as on the forward movement of the lathe on account of the slack, 
or lost motion, in the gears. 

This first cut is taken to prove that the lathe is properly 
geared, so the work should be measured with a rule, or screw 
p^tch gauge. 

Adjust the screw at K until the tool can be moved in deeper 
for the next cut and repeat the operation until the thread is 
nearly finished. Then the tool should be reset so that it will cut 
on only one side at a time. 

Finishing Side of Thread. — When roughing out the threads, 
the tool cuts on both sides of the po.nt since it is fed straight into 
the work. It is much easier, though, to finish the threads smooth 
if the tool cuts on one side only. This is done by rapping the end 
of the tool holder so that it is turned in the tool post just enough 
to change the position of the point of the tool about .01, or .02 of 
an inch. 

To prove that the tool is set over the proper amount, turn the 



IQ ELEMENTARY LATHE PRACTICE. 

lathe forward by hand a few revolutions, to take out all the slack, 
or lost, motion in the gears, then move the tool into the groove of 
the thread until one side just touches the side of the thread. The 
o^her side of the tool should then be about .01, or .02 of an inch 
away from the side of the thread. 

After the tool is properly adjusted, set the stop K. The tool 
is then drawn back and the lathe reversed until the tool is at the 
end of the work ready for a cut. It usually requires several fin- 
ishing cuts to take out all the rough marks left by the roughing 
cuts. 

When this side of the thread is finished, the other side is fin- 
ished in the same manner. 

If the lathe is provided with a compound rest, a somewhat 
different procedure is usually followed since the rest can be set 
at an angle of 30 degrees with the work, as in Fig. 18. 

In this case the tool is moved in by turning the small hand- 
crank M until the side at has been cut to the proper depth. 
While making these first cuts, the stop K is merely used to bring 
the cross-rest to the same position each time. The tool is then 
drawn back slightly with the hand-crank M and the stop K ad- 
justed so that the tool can be moved straight in by means of the 
hand-crank Q. This will finish the other side of the thread at P. 

To determine when the thread is cut to the proper size the 
work is removed from the lathe and tested with a standard nut 
having U. S. S. threads. 

After the threads are cut on this end of the exercise, it is re- 
versed in the lathe and the other end threaded in a similar man- 
ner. 

To prevent the screw of the dog from marring the portion 
already threaded two nuts should be screwed on and the dog fast- 
ened to the nuts. 

How to Reset the Tool. — ^When cutting threads of this size and 
larger, the tool usually becomes dull from taking the heavy rough- 
ing cuts. It is then necessary to resharpen it before taking the 
fine finishing cuts. 

To reset the tool in the lathe first get the angles correct, as 
shown in Fig. 16. Then revolve the lathe forward by hand to 
take up the slack in the gears and move the tool in close to the 
threads. If the tool is in a position so that it will cut too much 
off one side of the thread, it may be changed by disengaging the 
reversing gears with the lever R and turning the lathe hy hand. 



ELEMENTARY LATHE PRACTICE. 



17 



When the tool is in the proper position relative to the groove of 
the thread, the reverse gear lever R is reset. 

In a case where the tool is off the desired position only a very- 
little, it may be corrected by the rapping process. 

If the lathe has a compound rest the tool may be brought to 
the correct position by turning the hand-crank M. 

It would be well for beginners to practice thread cutting on a 
piece of scrap steel before trying to cut them on the exercise. 

EXERCISE No. 3. 



CAST IRON FINISHED ALL OVER. 




Sequence of Operations : 

1. Finish the inside of Piece A. 

2. Drill and Ream the hole in Piece B. 

3. Mount B on mandrel and finish outside. 

4. Screw A on B and finish the outside of A. 

Piece A. 

10 Thrds per l" U.S.S. 




:2 -4^f 

Fig. 19 
Rough Casting 




Fig 20 
Finished Casting 



18 



ELEMENTARY LATHE PRACTICE. 



USE OF 4-JAW CHUCK. 

To machine the inside of piece A it is necessary to hold it in 
the lathe by means of an independent four- jaw chuck, as shown 
in Fig. 21. Work of this kind is usually chucked so that the out- 




side surfaces will be within 1/32 of an inch of running true. 
The process of chucking the work is as follows : 

Centering Work in the Chuck. — Place the work in the chuck 
and adjust the jaws until they are all at approximately equal 
distances from the circles on the face of the chuck. Then put a 
cutting-off tool loosely in the tool post and move it close to the 
work and as near as possible to the end of the chuck jaws. Re- 
volve the lathe by hand to prove if the work is centered. If it is 
not centered to within 1/32 of an inch, readjust the jaws until it 
is. Now move the cutting-off tool to the end of the work and 
turn the lathe by hand. If the end runs out of true, rap it with a 
hammer at such points as will correct its position. 

Advantage of Proper Chucking. — Fig. 21 shows the work held 
by the middle step of the cone. One reason for holding it in this 
way is to permit the rough turning of the larger step while in 
the chuck. If the work were held by the small end, it would be 
apt to work loose when taking the heavy roughing cuts on account 
of the distance that the work projects out and the small diameter 
on which the chuck grips compared with that of the large end 
which is to be turned. 

ROUGH TURNING AND BORING. 



After the work has been properly chucked, rough turn the 
end and the largest diameter to within 1/32 of an inch of the fin- 
ished size. 

All cast iron has a hard surface, or scale, from 1/64 to 1/32 
of an inch deep so that it is necessary to run the lathe slower 
for the first cut than for those made after the scale has been re- 



ELEMENTARY LATHE PRACTICE. 



19 



moved. In taking this first cut the tool should be set deep 
enough to permit the point to cut under the scale. 

Speed of Lathe. — The speed of the lathe in taking the rough- 
ing cut on work of this size should be about right if the belt is on 
the smallest step of the cone and the back gears are used. After 
the scale is removed, the lathe may be run faster. 

A beginner will require experience before being able to de- 
termine the proper speeds and feeds for the diffrent kinds of 
lathe work. 

Advantage of Roughing Inside.— As the inside of piece A must 
fit the outside of the piece B, the 1 1/8 inch hole, the threads, 
and the taper must be machine true with each other, or else A will 
not fit into B properly. Now if the taper should be finished and 
the work moved in the chuck before the threads and the 1 1/8 
inch hole are finished, they would not be true with each other. 
For this reason it would be well to rough bore the inside to within 
1/32 of an inch of the finished size before any of these three parts 
are finished. 

Roughing Inside. — To rough bore the taper use a regular turn- 
ing tool. Set the compound rest to the correct angle and feed the 
tool in at that angle. 

If the lathe is not provided with a compound rest, the taper 
may be rough bored by turning both feeds by hand and following 
the cored surface as closely as possible. 

The cored hole in the rough casting, Fig. 19, is 15/16 of an 
inch in diameter which allows 3/16 of an inch for finishing the 
1 1/8 inch hole and 5/16 for the portion where the threads are to 
be cut. 

Use of Flat Drill. — To rough bore the hole a 1 1/16 flat, or 
lathe, drill is used as shown in Fig. 21. The holder A is clamped 
in the tool post so that the slot in it will hold the drill at the cen- 
ter of the lathe. If the drill is held above or below the center, the 
hole will be drilled larger than the drill. To prove that the slot 
in the holder is at the center, move it close to the tail-stock center. 
'After the holder is properly set, move it as close to the work as 
possible and feed the drill into the exercise by turning the hand 
crank on the tail-stock. 

This drill removes the hard surface, or scale, and also trues 
up, or centers, the hole to within 1/64, or 1/32 of an inch. Now 
enlarge the portion of the hole where the threads are to be cut 
with a 1 3/16 drill. 



20 



ELEMENTARY LATHE PRACTICE. 



To determine when this drill has been fed in far enough, mark 
on the drill with a piece of chalk the distance from the end of the 
work to the point where the recess is to be cut. By sighting 
across the end of the work the operator can then see when the 
drill has been fed in the proper distance. 

Use of Boring Bar. — To cut the square shoulder where the 
threads begin and the recess where they end, use a tool and boring 
bar, as shown in Fig. 22, held in the tool post. The width of this 



Fig. 22 



TI 






tool is 5/32 of an inch so that it will be necessary to take two cuts 
to make the recess Wide enough. Such a narrow tool is used be- 
cause it is less liable to chatter. 

This tool is ground with clearance at the sides as well as at 
the front and it should also be noticed that it is wider at the cut- 
ting edge than back close to the boring bar. This is done so that 
when the tool is fed into the work there will be little, or no chance 
of its binding on the side. 

To obtain the correct setting for the tool, move the boring bar 
into the hole and bring it up close to one side. The tool should 
then be adjusted until its cutting edge is parallel to the elements 
of this surface. 

The work is now all roughed out so that it makes very little 
difference which of the three fitting parts is finished first. 

FINISHING INSIDE 



The 1 1/8 inch hole has been drilled with a 1 1/16 inch lathe 
drill, but as such a tool cannot be relied upon to drill true to cen- 
ter, or size, it is necessary to turn it out with a boring tool. With 



ELEMENTARY LATHE PRACTICE. 



21 



this tool the hole can be bored true to center and within .01 of an 
inch of the finished size. 

The boring bar used in this case is the same as shown in Fig. 
22, but the cutter has a rounded point and is similar to the tool 
used for outside turning except that it is ground with less clear- 
ance. 

To insure accuracy and conserve time, the hole is then finished 
with a shell reamer held in the lathe as shown in Fig. 23. 




Reaming the Hole. — Before starting the reamer, the hole 
should be bored at the end, for a distance of about 1/8 of an inch, 
to the size which will just permit the reamer to enter. This dia- 
meter must be calipered very carefully and should be tested with 
the reamer itself. The rest of the hole is then bored about .01 of 
an inch smaller in diameter to allow enough material for finish- 
ing with the reamer. Since the reamer used in this case cuts on 
the sides as well as on the end, the hole must be bored true to cen- 
ter in order to be reamed true. 

If the reamer has a tapered shank, it is held in the lathe by a 
square shank socket and wrench, as shown in Fig. 23, and is fed 
into the work by turning the hand-crank on the tail-stock. 

In case the reamer has a straight shank, it is held as shown in 
Fig. 24. Here a dog is fastened to the end of the reamer and pre- 




vented from turning by a tool clamped at an angle in the tool- 
post. The end of the tool presses against the dog near the shank 
of the reamer so that as the reamer is fed into the work the car- 
riage of the lathe is forced along with it. This causes the tool 



22 ELEMENTARY LATHE PRACTICE. 

to hold the end of the reamer against the center of the tail-stock. 
When reaming work in a lathe, if the tail-stock is off center 
the hole will be reamed too large at the front end. 

Accurate Boring with Boring Bar. — In turning out holes with 
a boring bar, if all the cuts are started from one end, that end will 
be bored larger than the other. In case the hole is to be reamed, 
the reamer will correct this, but if the hole is to be finished with 
the boring bar It will be necessary to bore the hole from both ends. 
Th s is done by reversing the feed of the carriage. 

Speed of Lathe. — The speed of the lathe for reaming should be 
slow^er than when using the boring bar. If the belt is on the sec- 
ond smallest step of the cone with the back gears in, the lathe 
Lhould ha\e about the right speed for reaming. When using the 
boring bar. the belt should be on the largest step of the cone with- 
out the back gear. 

INSIDE THREADING 

The inside threads are cut in very much the same manner as 
the outside ones. The cutting tool is held in the boring bar and, 
like all boring tools, is ground with less clearance than tools used 
for outside work. 

To regulate the depth of each cut, the screw in the adjustable 
stop is placed between the stop and the cross-rest. Then by turn- 
ing the screws in after a cut has been taken the cross-rest can be 
draw^n back to permit a deeper cut with the tool. 

Cause of Threads Breaking. — When cutting threads in cast 
iron, they will break if the roughing cuts are too heavy and are 
liable to if they are cut to a sharp point. Another cause for the 
breaking of cast iron threads is the use of a dull tool, or one wdth 
too little clearance. 

Finishing Threads. — As a general rule cast iron is machined 
without using a lubricant, but in finishing threads a little lard oil 
will aid in producing a smooth finish. 

FINISHING ENDS 

The end of the work may be finished by taking a very light 
cut with the turning tool and then scraping it with a lathe scrap- 



ELEMENTARY LATHE PRACTICE. 



23 



er, as shown in Fig. 25. To provide a rest for the scraper a tool 




is clamped in the tool-post and as close as possible to the surface 
being scraped. 

A scraper is usually made from an old file ground smooth on 
the two sides and with a little clearance at the end. 

FINISHING TAPER 



To finish the taper, set the compound rest at an angle of 30 
degrees with the axis of the lathe. Such a rest is normally at 
right angles with the lathe axis so that it must be turned through 
60 degrees to cut the 30 degree angle. A regular turning tool 
may be used to finish this angle, but it should be set so that the 
straight side will be nearly parallel with the tapered surface. 

If the lathe is not provided with a compound rest, the angle 
may be cut with the side of a tool set at the proper angle. To set 
this tool, use the thread and center gauge, as shown in Pig. 26. 

In case the angle is any other than 30, or 60 degrees, it is 
necessary to set the tool with a bevel and bevel protractor. 

After the taper has been cut, it may be finished smooth by 
scraping with a lathe scraper in very much the same manner as 
shown in Fig. 25. The tool that is used as a rest is set in as close 
as possible to the taper. If this rest is too far away from the sur- 
face being finished, the scraper will chatter leaving a rough sur- 
face. 



24 



ELEMENTARY LATHE PRACTICE. 



Piece B. 





Thrds. per 1 


US 

*MttlW 







|TL 






i 1 


'f 


, 7 




Rough Casting Fig. 27 Finished Casting 

DRILLING AND REAMING. 

This piece is f rst placed in the chuck, as shown in Fig. 28, 
and the end rough turned to see if it is a good casting. The hole 




rig. 28 



is then drilled with a 23/32 inch twist drill and reamed out to 
size with a 3/4 inch rose reamer. 

Centering Twist Drill. — This drill will not bore a hole in the 
center unless the point is controlled in some way. To do this, a 
cutting-off tool is clamped in the tool-post with its point well 
above the center of the lathe and is then moved close to the point 
of the drill. As the drill starts to cut, it wabbles a little on ac- 
count of the po.nt being off center. The cutting-off tool is then 
gradually brought against the drill which is at the same time be- 
ing slowly fed into the work by turning the hand crank on the 
tail-stock. It is necessary to have the drill centered true before it 
begins to cut the full diameter. 

The drill should be placed in the tail-stock so that the cutting 
edges are vertical. If they are horizontal, it will be difficult to 
make the drill center. 

If the hole in this piece were larger, it would be cast with a 
core and then machined in the same manner as the 1 1/8 inch hole 
in piece A, but since it is cast solid, the hole can be machined 
more advantageously by using a twist drill and a rose reamer. 

Reaming. — After the hole has been drilled with the 23/32 



ELEMENTARY LATHE PRACTICE. 



25 



dr Jl, bore it out with a small boring tool for about 1/8 of an inch 
from the end to the diameter that will just fit over the reamer 
and insure its starting true. Ream the hole with the reamer held 
in the same manner as the twist drill in Fig. 28. 

Speed of Lathe. — The lathe should run slower for reaming 
than for drilling. The speed will be about right for this size 
reamer if the belt is on the largest step of the cone without the 
back gears being used. The speed for the drill may be much 
faster. With a high-speed steel drill, the belt can be run on the 
second smallest step of the cone. If the drill is made of carbon 
steel, a slower speed should be used. 

Advantage of Rose Reamer. — In drilling long holes like this, 
the drill is very apt to get off center a little as it is fed deeper into 
the work, even though it may have been started dead true. 

The reamer used in this case is called a rose reamer, or rose 
bit. and cuts on the end only. For this reason, if the hole is ap- 
proximately true, say within 1/64 of an inch, it will ream the hole 
straight and true to size if it is once started true. 

FINISHING CORNER 



After the hole is bored and reamed, the work may be finished 
at the end by using a tool ground like a threading tool, but hav- 
ing an angle at the point a little less than 90 degrees, as in Fig. 
29. 




The boss, or hub, which is 1 8/8 inches in diameter, is finished 
with one cutting edge of this tool set nearly parallel to the work, 
the point being a trifle deeper than the rest. This will insure the 
full depth of cut for the entire length and also a good sharp cor- 
ner. The direction of feed for this tool should be from the end 
and towards the square corner or shoulder. Tf it is fed in the op- 
posite direction the tool is apt to chatter. 

This tool is also used to finish the end, but it is turned a little 



26 



ELEMENTARY LATHE PRACTICE. 



in the tool-post so that the other cutting edge is nearly parallel 
to the surface to be cut. After using this tool, the work may be 
finished smoother by scraping the ends, as in Fig. 25, and by filing 
the boss, or hub. 

USE OF MANDREL, OR ARBOR 

Before this piece can be finished on the outside, it must be 
forced on a mandrel, or arbor, and placed in the lathe, as shown 
in Fig. 30. Most commercial shops are provided with hardened 




steel mandrels for this purpose, but if one is not available it can 
be made from soft steel in the following manner: 

Making Mandrel. — Cut off a piece of steel of suitable length, 
say 6 inches, and rough turn it to within 1/32 of an inch of the 
jdiameter of the hole. Then turn it at the end for a distance of 
about 1/8 of an inch to the size that will just fit the hole. The 
rest of the distance is now turned .002, or .003 of an inch larger 
and filed for about 3 inches until it will just fit the hole. The 
next 2 inches are filed with a slight taper so that when the man- 
drel is pressed into the hole it will fit tight enough to hold the 
casting while t is be^ng turned. This kind of a fit is called a 
forced, or driving fit. 

When making such a mandrel, it is not necessary to turn that 
portion to which the dog is fastened. 

Mounting Work on Mandrel. — Before pressing the mandrel in, 
it should be oiled to prevent it from being marred, or scored. 
Mandrels are usually forced in with a mandrel press, but if one 
is not available, they may be driven in with a hammer. When 
this method is used, a piece of lead, or some other soft material, 
must be held on the end of the mandrel to keep the hammer from 
marring the center. 

FINISHING OUTSIDE OF PIECE B TO FIT A 

This casting is rough turned to within 1/32 of an inch of the 
finished size before any part of it is finished The 1 1/8 inch end 
is then turned until it fits the corresponding part of the hole in 



ELEMENTARY LATHE PRACTICE. 



27 



piece A as closely as possible and yet not so tight that it cannot 
be freely rotated. This kind of a fit is called a close running fit. 

Cutting Threads.— The portion to be threaded should be 
turned a little smaller than the diameter at the bottom of the 
threads in piece A. This size is measured by means of the inside 
spring-thread calipers. 

There is no recess, or groove, cut at the end of this thread so 
that if the threading tool is allowed to travel farther than the end 
of the preceding cut. either the point of the tool or the threads 
may break. To prevent this, the lathe is stopped when the tool is 
within a half a thread of the end and the cut finished by turning 
the lathe by hand. In this way the lathe is kept under control 
and the tool may be drawn back when it reaches the end of the 
preceding cut. Experienced lathe operators do not, as a rule, 
turn the lathe by hand, but control the lathe entirely by the 
shipper. 

The speed of the lathe for cutting this thread will be about 
right for beginners if the belt is on the second smallest step of the 
cone and the back g^^p.rs are thrown in. 

Finishing' the Angle, or Taper. — The 30 degree angle may be 
cut by setting the compound rest to the correct angle and using a 
regular turning tool. In case the tool leaves a few tool marks, 
they may be removed by f.ling. 

If the lathe is not provided with a compound rest, this angle 
may be cut by setting a square-nose tool, as in Fig. 31, with the 




aid of a thread gauge. Any other angle would have to be set 
with a bevel and bevel protractor. 

This tool is not as wide as the surface to be cut because one 
that will cut the full width is very liable to chatter. It is there- 
fore better to make several cuts with a narrow tool. The surface 
can then be finished smooth by filing. 

The closeness of the fit of this taper with that in A can be 



2g ELEMENTARY LATHE PRACTICE. 

tested by rubbing black paint, which consists of lamp black and 
oil, on the tapered surface in A. When B is screwed into A, 
marks will be made on B indicating the high spots. If these are 
not too high, they may be removed by filing. 

FINISHING OUTSIDE OF PIECE A. 

Piece A may now be screwed on B and the outside rough 
turned to within 1/32 of an inch of the finished size. 

The ends of the different steps are finished to the proper 
length with the tool shown in Fig. 29. This same tool can then be 
used to turn the different diameters to within 0.002 or 0.003 of an 
inch of the required size. These steps are brought to the final 
size by filing. 

Filing. — The file for this work should be less than 1 inch in 
width. If it is wider than the steps, a beginner will usually file 
the portion at the end of each step smaller in diameter than that 
which is close to the square corners. 

The different diameters may be measured accurately with the 
micrometer calipers. 

KNURLING 

After piece A is finished, it is removed from B and B is re- 
versed in the lathe so that the boss may be knurled. 

In case there is enough room between the dog and the work, 
when held as in Fig. 30, there is no need to reverse the work for 
knurling since it can be done in this position. 

The boss at the end of B is used as a handle so that if it were 
left smooth it would be hard to turn by hand. The surface is 
therefore made rough with a knurling tool as shown in Fig. 32. 



Fig. 32 




The speed of the lathe should be about the same for knurling 
as for thread cutting. If the lathe runs too fast, the knurling tool 
does not cut satisfactorily. 

The tool is set so that the face of the rollers is parallel with 



ELEMENTARY LATHE PRACTICE. 29 



the surface to be knurled. When starting the cut, the rollers can 
be forced into the piece easier if about half of their width extends 
past the end of the work. 

The knurling tool should be pressed into the work fast enough 
so that about one half the depth of the finished knurl will be cut 
while the lathe makes three or four revolutions. If the tool is 
forced in too slow, it will cut a finer knurled surface than the 
rollers are intended to cut. 

The tool is fed along the surface in the same manner as in 
plain turning. The speed at which the carriage of the lathe moves 
has no effect upon the pitch of the knurled surface since this is 
controlled by the pitch of the grooves in the rollers. If a finer 
knurled surface is desired, a knurling tool having rollers with 
finer grooves would have to be used. 



